WM8904
Pre-Production
DIGITAL-TO-ANALOGUE CONVERTER (DAC)
The WM8904 DACs receive digital input data from the DACDAT pin and via the digital sidetone path
(see “Digital Mixing” section). The digital audio data is converted to oversampled bit streams in the
on-chip, true 24-bit digital interpolation filters. The bitstream data enters two multi-bit, sigma-delta
DACs, which convert them to high quality analogue audio signals. The Wolfson SmartDAC™
architecture offers reduced power consumption, whilst also delivering a reduction in high frequency
noise and sensitivity to clock jitter. It also uses a Dynamic Element Matching technique for high
linearity and low distortion.
The analogue outputs from the DACs are sent directly to the output PGAs (see “Output Signal Path”).
The DACs are enabled by the DACL_ENA and DACR_ENA register bits.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R18 (12h)
Left DAC Enable
3
DACL_ENA
0
Power
Management
6
0 = DAC disabled
1 = DAC enabled
Right DAC Enable
0 = DAC disabled
1 = DAC enabled
2
DACR_ENA
0
Table 32 DAC Enable Control
DAC DIGITAL VOLUME CONTROL
The output level of each DAC can be controlled digitally over a range from -71.625dB to 0dB in
0.375dB steps. The level of attenuation for an eight-bit code is detailed in Table 34.
The DAC_VU bit controls the loading of digital volume control data. When DAC_VU is set to 0, the
DACL_VOL or DACR_VOL control data is loaded into the respective control register, but does not
actually change the digital gain setting. Both left and right gain settings are updated when a 1 is
written to DAC_VU. This makes it possible to update the gain of both channels simultaneously.
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
DESCRIPTION
R30 (1Eh)
DAC Volume Update
8
DAC_VU
N/A
DAC Digital
Volume Left
Writing a 1 to this bit causes left
and right DAC volume to be
updated simultaneously
Left DAC Digital Volume
00h = Mute
7:0
DACL_VOL [7:0]
1100_0000
(0dB)
01h = -71.625dB
02h = -71.250dB
… (0.375dB steps)
C0h to FFh = 0dB
(See Table 34 for volume range)
DAC Volume Update
R31 (1Fh)
8
DAC_VU
N/A
DAC Digital
Volume Right
Writing a 1 to this bit causes left
and right DAC volume to be
updated simultaneously
Right DAC Digital Volume
00h = Mute
7:0
DACR_VOL [7:0]
1100_0000
(0dB)
01h = -71.625dB
02h = -71.250dB
… (0.375dB steps)
C0h to FFh = 0dB
(See Table 34 for volume range)
Table 33 DAC Digital Volume Control
PP, Rev 3.3, September 2012
66
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
